Switching Rate and Dwell Time of Hybrid Selection-Maximal Ratio Combining in Rayleigh Fading Channels

Many investigations of hybrid selection (HS) diversity assume maximal ratio combining (MRC) of the selected branches. However, a coherent detector needs to dwell on the received signal for some time before it can produce accurate channel estimates for fading compensation, a requirement that appears inconsistent with the branch switching that occurs in a selection diversity receiver. Motivated by this observation, we derive in this letter analytical results on the switching rate and average dwell time of a hybrid selection diversity receiver where M out of a total of N branches are selected for combining. As one would expect, the switching rate is proportional to the Doppler frequency, while the average dwell time is proportional to the duration of a fade cycle. More importantly, the results in the paper suggest caution in interpreting the results of performance analysis of idealized HS/MRC structures. They also shed some light on the demodulator design in these systems